1. Field of the Invention
The present invention relates to an information recording medium used for a reproducing apparatus and a recording apparatus, which read out information from the information recording medium with making it move relatively, particularly, relates to an information recording medium to be recorded and/or reproduced by an optical device.
2. Description of the Related Art
Until now, recording and reproducing information by using a laser beam or like has been performed by an optical disc system.
There existed a DVD (Digital Versatile Disc) as one of information recording mediums used for such an optical disc system. Such a DVD disc has an information recording surface composed of an information track and an information pit array, which are engraved in a rugged shape on a surface of a transparent plastic substrate having a thickness of 0.6 mm and a diameter of 120 mm by a forming process. The information track is provided for recording information, and the information pit array is provided for reproducing the information by scanning the pit array.
In a case of a reproducing type information recording medium, a reflective layer composed of a high reflectivity film such as gold and aluminum is formed on an information recording surface. Further, in a case of a recording type information recording medium, a dye film is formed on the information recording surface.
With respect to a recording type information recording medium formed with a dye film on the information recording surface, there is provided a DVD-R (Digital Versatile Disk-Recordable) as a recordable information recording medium. Furthermore, there is provided a rewritable information recording medium, which is formed with magneto-optical recording film on the information recording surface.
FIG. 32 is a cross sectional view of a conventional recording type DVD-R disc.
Such a DVD-R disc mentioned above is actually composed a structure shown in FIG. 32. In FIG. 32, a DVD-R disc 70 is composed of a transparent plastic substrate 71 having an information recording surface 710 on its surface, a recording layer 72, an adhesive layer 73 and a dummy substrate 74. The recording layer 72 and the adhesive layer 73 are laminated on the substrate 71 in order, and then the dummy substrate 74 is affixed on the adhesive layer 73. The information recording layer 710 is further composed of an information track and an information pit array, which are engraved in a rugged shape.
Generally, a convex shaped section, which projects into a side to be irradiated by a laser beam for recording and reproducing, is applied for an information track. In the convex shaped section, an information track composed of a groove and address information composed of a pit are formed as a continuous line or as an intermittent pit array with respect to a scanning direction of a laser beam. These information track and address information are formed by a forming method of a so-called stamper method. The intermittent pit array is provided for a user to record information in a predetermined information track accurately by positioning the predetermined information track.
According to a manufacturing method of recording type DVD-R disc by the stamper method, an information track and address information, which are formed by a cutting method, are provided in a concave shaped section “AA” of the substrate 71 as shown in FIG. 32.
The recording type DVD-R disc 70 is recorded and reproduced by irradiating a laser beam “LB” having a wavelength of 635 nm on the information recording surface 710 from the substrate 71 side. In other words, the laser beam “LB” is irradiated on the concave shaped section “AA” of the substrate 71, and then the recording type DVD-R disc is recorded and reproduced.
The concave shaped section “AA” and a convex shaped section “BB” of the substrate 71 are referred to as a groove and a land respectively.
FIG. 33 is a cross sectional view of a next generation type information recording medium having higher density than a current DVD disc. Such a next generation type information recording medium has been developed actively. In FIG. 33, a next generation type information recording medium 75 in high density is composed of a substrate 71 having an information recording surface 710 in a rugged shape on its surface, a recording layer 72 and a light transmitting layer 76 having a thickness of 0.1 mm, wherein they are laminated in order. The substrate 71 is made of a transparent plastic disc having a thickness of 1.1 mm and a diameter of 120 mm and manufactured by the stamper method as the same method as for a DVD disc. The next generation type information recording medium 75 is recorded and reproduced by irradiating a laser beam “LB” having a wavelength of 400 nm on an information track of the information recording surface 710 and a concave shaped section “AA” or a groove of the substrate 71.
That is to say, in either of the recording type DVD-R disc 70 and the next generation type information recording medium 75, recording and reproducing is performed with respect to the concave shaped section “AA” on the substrate 71. When viewing from a different angle, in the case of the recording type DVD-R disc 70, information is recorded on and reproduced from a concave shaped section, which projects into a side to be irradiated by a laser beam for recording and reproducing. On the contrary, in the case of the next generation type information recording medium 75, information is recorded on and reproduced from a convex shaped section, which becomes dented with respect to a side to be irradiated by a laser beam for recording and reproducing.
In other words, a groove to be an information track becomes projected into a side to be irradiated by a laser beam for recording and reproducing with respect to the recording type DVD-R disc. However, in the case of the next generation type information recording medium 75, the groove becomes dented with respect to a side to be irradiated by the laser beam.
Inventors of the present invention have actually performed recording and reproducing of such a next generation type information recording medium 75 in high density. The inventors founded a problem such that an output of reproduced signal has decreased and resulted in deterioration of information quality and an error rate of reproduced signal increased when information has been recorded in the concave shaped section “AA”, which is a groove of the substrate 71, in comparison with recording and reproducing the convex shaped section “BB”, which is a land of the substrate 71.
Further, since an information signal recorded in the concave shaped section “AA” has been deteriorated in quality, recording in high density could not be performed. Such deterioration of quality is supposed to be caused by that a direction of thermal diffusion in the recording layer 72 turns around.
In order to deal with the phenomenon, it is considered that information is recorded on the convex shaped section “BB” as a land and reproduced. However, an address to be reproduced were interfered and resulted in another problem such that accurate address information itself could not be reproduced.